Field of the Invention
The present invention is related to an apparatus and method which record and/or reproduce information on an optical information recording medium by using holography.
Description of the Related Art
Through a BLU-RAY DISC™ specification using a blue-violet semiconductor laser, at present, commercialization of optical disk having recording density of about 100 GB is presently performed. From now on, large capacity greater than 500 GB is expected from optical disk recording. However, for realizing the above-described ultra-high density by using an optical disk, a high-density technology is needed through another method which is different from a high-density technology using the conventional short wavelength and high numerical aperture of objective lens.
Holographic Data Storage System (HDSS) has been considered as one of promising candidates for future Optical Data Storage (ODS) systems. HDSS can record an encoded data page with around a couple million pixels with a single light pulse. Furthermore, hundreds of data pages can be multiplexed at the same location in the media. HDSS has a high possibility of becoming a Post BD system.
However, tolerances of HDSS to physical perturbation such as mechanical instability needs to be stringent in return for the associated high density recording. Especially, the tolerances of HDSS using angularly multiplexed recording will be stringent because of the narrow Bragg selectivity associated with the utilized off-axis optical configuration.
U.S. Pat. Appl. No. 20090129234 (the entire contents of which are incorporated herein by reference) describes a hologram recording device which illuminates with a recording beam (S) a hologram recording medium (B), and which illuminates with a reference beam (R) a region illuminated with the recording beam (p) while variably controlling the incident angle regarding the hologram recording medium (B).
Compensation techniques for reducing the degradation of recording/reading of the hologram have been described. For example, Muroi et al., published “Optical compensation of distorted data image caused by interference fringe distortion in holographic data storage,” in Appl. Opt. 48(19), 3681-3690 (2011), the entire contents of this publication are incorporated herein by reference. In this publication, an optical compensation method using adaptive optics for the distortion of interference fringes in the holographic medium. A genetic algorithm is employed to control the adaptive optics with a deformable mirror.